This sounds like an incompatibility issue to be completely honest. Doesn't have to be a deal-breaker per se, but I do think if you can't find some kind of common ground or at least an understanding here this could lead to bigger problems later on.

I'm with you on the somewhat nihilistic worldview (also a woman) but I don't think that's a negative. It can actually help you appreciate life more, live in the moment more, be more conscious of the immediate effects you have on the people around you. It can have surprisingly optimistic outcomes for how cynical it all sounds on the surface.

Unfortunately to someone who doesn't see it that way at all it can be a wildly depressing worldview, especially if that person is religious or otherwise has deeply spiritual beliefs that assign meaning to life. They don't have to clash. She's going to have to understand that the way you make sense of the world has no bearing on how you feel about her.

It could absolutely have to do with the way you communicate too, but ultimately you don't want to end up in a situation where you feel like you have to tiptoe your way around certain subjects in order to not upset your partner. It doesn't make her "too sensitive" just as it doesn't necessarily make you tactless, again it's just an incompatibility issue then.